The Evolved Packet System (EPS) of the 3rd Generation Partnership Project (3GPP) is composed of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW or PDN GW), a Home Subscriber Server (HSS), an Authentication, Authorization and Accounting (AAA) server of 3GPP, a Policy and Charging Rules Function (PCRF) entity and other supporting nodes.
FIG. 1 is a schematic diagram illustrating the system architecture of the EPS according to the related art. As shown in FIG. 1, the MME is responsible for the related work of control plane, such as the mobility management, the processing of non-access stratum signaling and the management of user mobility managing context; the S-GW is an access gateway device connected with the E-UTRAN, which forwards data between the E-UTRAN and the P-GW, and is responsible for caching the paging waiting data; the P-GW is an edge gateway between the EPS and the Packet Data Network (PDN), and is responsible for functions such as the access of the PDN and the data forwarding between the EPS and the PDN; the PCRF is a policy and charging rules function entity, it is connected with the Internet Protocol (IP) service network of an operator via a receiving interface Rx and acquires the service information, and in addition, it is connected with the gateway device of the network via a Gx/Gxa/Gxc interface, and is responsible for initiating the establishment of IP bearers, for guaranteeing the Quality of Service (QoS) of service data, and for performing the charge control.
The EPS supports the interconnection with a non-3GPP system, wherein the interconnection with the non-3GPP system is implemented via an S2a/b/c interface; the P-GW serves as an anchor point between the 3GPP system and the non-3GPP system. In the system architecture diagram of the EPS, the non-3GPP system is classified into a trusted non-3GPP IP access and an untrusted non-3GPP IP access. The trusted non-3GPP IP access can be connected with the P-GW via an S2a interface directly; while the untrusted non-3GPP IP access needs to be connected with the P-GW via the Evolved Packet Data Gateway (ePDG); the interface between the ePDG and the P-GW is S2b; S2c provides the control and the mobility supporting related to user plane between the User Equipment (UE) and the P-GW, the supported mobility management protocol is Mobile IPv6 Support for Dual Stack Hosts and Routers (DSMIPv6).
In the 3GPP network before the EPS, the Policy and Charging Enforcement Function (PCEF) entity resides in the P-GW; the control of all functions may be completed as long as there is an interface between the PCRF and the P-GW; the information is exchanged between the PCRF and the P-GW via a Gx interface (as shown in FIG. 1). When the interface between the P-GW and the S-GW is based on Proxy Mobile IPv6 (PMIPv6), there is further a Bearer Binding and Event Report Function (BBERF) entity in the S-GW for performing the QoS control for service data flows; the information is exchanged between the S-GW and the PCRF via a Gxc interface (as shown in FIG. 1). When accessing via the trusted non-3GPP access, there may also be a BBERF which resides in the trusted non-3GPP access gateway. The information is exchanged between the trusted non-3GPP access gateway and the PCRF via a Gxa interface (as shown in FIG. 1). When a UE roams, an S9 interface serves as the interface of the home PCRF and the visit PCRF, provides the UE with the Application Function (AF) of the service at the same time, and sends the service information which is used for instituting a Policy and Charging Control (PCC) policy to the PCRF via an Rx interface. The EPS system supports Multiple PDN access, i.e. the UE may access multiple PDNs simultaneously via multiple P-GWs or one P-GW, the EPS also supports that a UE may access the same PDN multiple times simultaneously. In the 3GPP, the corresponding PDN network may be found according to the Access Point Name (APN). Therefore, it can be considered that a UE may access the same APN for multiple times simultaneously. A connection from a UE to the PDN network is usually referred to as an IP Connectivity Access Network (IP-CAN) session; therefore, the EPS supports that a UE may have multiple IP-CAN sessions with the same PDN network simultaneously.
FIG. 2 is a flowchart illustrating the initial attachment for a UE accessing the EPS via the trusted non-3GPP access network according to the related art. As shown in FIG. 2, the specific steps for a UE initially attaching to a PDN via the trusted non-3GPP access network are as follows.
Step S201, the UE accesses a trusted non-3GPP access network;
Step S202, after accessing the trusted non-3GPP access network, the UE requests the HSS/AAA to perform the EPS access authentication; after receiving the EPS access authentication request, the HSS/AAA authenticates the UE which sent the request; after finishing the authentication of the UE, the HSS/AAA sends P-GW selecting information subscribed for the UE and the APN subscribed for the UE, which includes the default APN, to the trusted non-3GPP access gateway;
Step S203, after the authentication is successful, the attaching process of layer 3 is triggered;
Step S204, the trusted non-3GPP access gateway in which a BBERF resides sends a gateway control session establishing request message to the PCRF, wherein the gateway control session establishing request message carries the Network Access Identifier (NAI) of the UE and the default APN;
Step S205, the PCRF institutes a PCC rule and QoS rule according to the network policy, the bearer attribute, the subscription data of the user and so on. meanwhile, corresponding event trigger may also be instituted; the PCRF sends the QoS rule and the event trigger to the trusted non-3GPP access gateway via a “gateway control session establishment acknowledge” message; the trusted non-3GPP access gateway installs the QoS rule and the event trigger;
Step S206, after receiving the P-GW selecting information, the trusted non-3GPP access gateway selects the P-GW according to the P-GW selecting information, and sends to the selected P-GW a proxy binding update message carrying the NAI of the UE and the default APN;
Step S207, after receiving the proxy binding update message, the P-GW in which the PCEF resides sends to the PCRF an indication of IP-CAN session establishing carrying the NAI of UE, the IP address which is allocated for the UE by the P-GW and the default APN;
Step S208, after receiving the indication of IP-CAN session establishing, the PCRF associates the indication of IP-CAN session establishing with the forgoing indication of gateway control session establishment according to the NAI of UE and the default APN, meanwhile, searches the subscription information of the UE, and updates the originally instituted rule according to the network policy, the bearer attribute, the subscription information of the user, and so on; the PCRF sends to the P-GW an IP-CAN session establishment acknowledge message carrying the PCC rule;
Step S209, after receiving the IP-CAN session establishment acknowledge message, the P-GW installs and executes the PCC rule carried in the IP-CAN session establishment acknowledge message, and sends its own IP address to the HSS at the same time;
Step S210, the P-GW returns a proxy binding acknowledge message to the trusted non-3GPP access gateway;
Step S211, if the QoS rule instituted in step S208 is different from that sent in step S205, the PCRF delivers the updated QoS rule to the trusted non-3GPP access gateway via a gateway control and QoS policy rule providing message;
Step S212, the trusted non-3GPP access gateway installs the QoS rule, and returns a gateway control and QoS policy rule providing acknowledge message;
Step S213, layer 3 attachment is completed;
Step S214, a PMIPv6 tunnel is established between the trusted non-3GPP access gateway and the P-GW; the UE may send or receive data; and the process is terminated.
When a UE establishes a second PDN connection with the default APN, the UE sends to the trusted non-3GPP access gateway a “new PDN connection establishing trigger message” carrying the default APN; the other steps are as shown in steps S204-S214. Every time a PDN connection is established, the P-GW allocates an IP address for the UE.
In the above process, the interaction between the trusted non-3GPP access gateway and the PCRF is before the interaction between the P-GW and the PCRF; at this time, the trusted non-3GPP gateway does not have the IP address which is allocated for the UE by the P-GW; regardless of the initial attachment or the second access or accessing the same PDN for multiple times, the trusted non-3GPP access gateway has only the NAI and the default APN when the trusted non-3GPP access gateway interacts with the PCRF. Since the NAIs and the default APNs are identical for multiple connections of the UE to the same PDN (or APN), the PCRF can not distinguish these multiple PDN connections according to such information, and thus can not associate the gateway control session message with the IP-CAN session message belonging to the same PDN connection.
However, for a PCRF, the gateway control session message and the IP-CAN session message belonging to the same IP-CAN session must correspond to each other one by one. The PCC rule includes the QoS control policy and the charging policy while the QoS rule only includes the QoS control policy. The charging policy of the PCC rule is associated with the provided QoS, that is to say, the charging policy installed in the PCEF must be associated with the QoS control policy installed in the BBERF. To guarantee the correct charging, the PCRF must guarantee that the BBERF has a successfully-activated QoS rule corresponding to the PCC rule successfully-activated in the PCRF. The corresponding PCC rule and QoS rule are delivered via the corresponding gateway control session message and the IP-CAN session message. Similarly, when a UE accesses the same PDN (or APN) for multiple times, there is also a problem in the existing switching technology. FIG. 3 shows the process that a UE is switched from accessing EPS via a trusted non-3GPP access network 1 to accessing EPS via another trusted non-3GPP access network 2. The wireless access technologies of the two trusted non-3GPP access networks are the same. The detailed steps are as follows.
Step S301, according to the process of FIG. 2, a UE accesses trusted non-3GPP access network 1, and establishes a PDN connection to the default APN via the access network;
Step S302, the UE finds trusted non-3GPP access network 2, and decides to initiate switching;
Step S303, after accessing trusted non-3GPP access network 2, the UE requests the HSS/AAA to perform the EPS access authentication; after receiving the EPS access authentication request, the HSS/AAA authenticates the UE which sent the request; after finishing the authentication of UE, the HSS/AAA sends the IP address of the P-GW selected by the UE via access network 1 and the APN including the default APN subscribed by the UE to trusted non-3GPP access gateway 2;
Step S304, after the authentication is successful, the attaching process of layer 3 is triggered;
Step S305, trusted non-3GPP access gateway 2 in which a BBERF resides sends a gateway control session establishing request message to the PCRF, wherein the gateway control session establishing request message carries the NAI of the UE and the default APN;
Step S306, the PCRF finds the information before the switching of the user according to the NAI of the UE and the default APN, associates the message with the session before the switching, and sends the corresponding QoS rule and event trigger to trusted non-3GPP access gateway 2 via a “gateway control session establishment acknowledge” message. The PCRF may also update the foregoing QoS rule and event trigger. Trusted non-3GPP access gateway 2 installs the QoS rule and the event trigger;
Step S307, trusted non-3GPP access gateway 2 sends to the P-GW a proxy binding update message carrying the NAI of the UE and the default APN;
Step S308, after receiving the proxy binding update message, the P-GW in which the PCEF resides sends to the PCRF an indication of IP-CAN session modification carrying the NAI of the UE, the default APN and the IP address which is allocated for the UE by the P-GW;
Step S309, after receiving the indication of IP-CAN session modification, the PCRF sends it to the P-GW via an IP-CAN session modification acknowledge message according to the PCC rule before the switching of the UE. The PCRF may update the originally instituted PCC and QoS rule. After receiving the IP-CAN session establishment acknowledge message, the P-GW installs and executes the PCC rule;
Step S310, the P-GW returns a proxy binding acknowledge message to the trusted non-3GPP access gateway;
Step S311, if the QoS rule updated in step S309 is different from that sent in step S306, the PCRF delivers the updated QoS rule to the trusted non-3GPP access gateway via a gateway control and QoS policy rule providing message;
Step S312, the trusted non-3GPP access gateway installs the QoS rule, and returns a gateway control and QoS policy rule providing acknowledge message;
Step S313, layer 3 attachment is finished;
Step S314, a PMIPv6 tunnel is established between trusted non-3GPP access gateway 2 and the P-GW; the UE may send or receive data; and the process is terminated.
In the process, when the PCRF receives the indication of gateway control session establishment carrying the NAI and the default APN in step S305, since it is the same as the message received when the UE accesses the APN again, the PCRF can not judge whether the UE is switched (i.e. the BBERF relocation occurs) or the UE requests to establish another PDN connection to the default APN.
The above two problems exist also in the prior art when the UE accesses from the E-UTRAN, and the PMIPv6 protocol is used between the S-GW and the P-GW. (1) the PCRF is unable to determine whether it is BBERF relocation or another PDN connection that the UE requests to establish to an APN when the PCRF receives the indication of gateway control session establishment. (2) it is unable to associate the IP-CAN session message and the gateway control session message related to the same PDN connection.